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...Water powered jet pack!...

Discussion in 'The Pub' started by Tweetster, Mar 2, 2011.

  1. wow... that looks like heaps of fun...
  2. As well as the engine and pump it's connected to.

    Seems to me you could achieve much the same thing by sticking a pole on a jetski and hanging a harness from that.
  3. I'm surprised he could go so high. From that distance the force of the water hitting the lake wouldn't be enough to hold him up.

    You would be better off with a tank of liquid hydrogen and oxygen. That would be water powered too. Would have to work out how to shield yourself from the heat though.
  4. :shock: :LOL:
    Obviously you're not familiar with Newton's laws of motion.
  5. 3rd law right? The force of the water hitting the ground = the force of holding the guy up. equal and opposite
  6. It doesn't make a difference whether the water hits the ground forcefully or weakly. Assuming everything else is kept constant, changing the height above ground does not alter the force of the water moving downwards from the jetpack and the equal and opposite upwards force on the jetpack.
  7. Lilley, how does a jet plane provide motive force?

    Where did they hide the pumper fire engine? :-k
  8. .... Under water!!:D. Think iceberg!!
  9. from the moving air hitting the still air and bouncing the plane forward.
  10. But if this were true jet aircraft would always fly as close as possible to sea level where there is denser air to push against.

    What Newton's law states is that when gas shoots out of the engine at a given force there is an equal force pushing the engine in the opposite direction. As long as that force is greater than anything trying pushing back (ie wind resistance and/or gravity) you get forward movement. So the thinner the air the less resistance it offers, and the more efficient the engine works. It's why really high level airspeeds are only achievable in the upper levels of the atmosphere.

    The only thing keeping that jetpack close to the water is the length (and weight) of the hose.
  11. Uh, you sure about that?

    Gases and liquids have mass too.

    How does a rocket work in space where there is no air to "bounce off"?
  12. hmm. sorry guys I was feeling a bit whimsical at the time of writing. My major is fluid/thermo dynamics. My grasp on the subject is satisfactory.

    gsxxer, I was thinking about that same scenario as a counterpoint this morning.
  13. [​IMG]
  14. yeh well, sue me.
  15. Surely you want to engage in a bit of self-flagellation...the courts need not be involved.

    They sure don't make Engineers like they used to. :p
  16. Only when the prize is worth it my friend, the appropriate time will come same as it always has in the past. I've certainly more than made a fool of myself around campus on occasion. To be frank my heart just wasn't in it this time, it was a sloppy effort even by the lowest standards.
  17. That's ok Lilley, you were thinking about Pelton wheels weren't you?
  18. (after googling pelton wheels) Actually I wasn't. It would be difficult to them to apply to this scenario anyhow. I was always considering it as a venturi meter but just playing dumb. It was how I used to think rockets and jets worked when I was a wee lad.

    As for the design, it's really quite poor. The amount of energy the pumps would take would be immense. And there would likely have to be two pumps, one to pump the water up and another to compress it once it's up. The use of water as the propellant is equally as daft, very hard to compress and does not expand at all upon decompression. The only thing it has going for it is the amount of the stuff around, but it would be useless on dry land - the only place that it could have a practical purpose. And if there is some crap in the water the pumps wont like that at all.
  19. I dont think the intention was practicality, its a chance to experience, albeit limited, what a real jetpack would be like.

    Basically noone has the money, skill or sanity to attempt to use a real jetpack. Untethered fuel-carrying jetpacks have a tiny range before needing refuelling.

    This thing looks like it could go for as long as you want. Looks fun to me.